Petroleum products, particularly crude oil, are stored in storage tanks, many of which are very large, holding 500,000 barrels of crude oil in some instances. Such tanks may exceed 250 feet in diameter. Crude oil stored in these tanks deposit sludges which accumulate on the bottom of the tanks resulting in operational problems and diminished capacity. Many methods have been devised to agitate or circulate the content of the tanks, simplify the cleaning of these tanks and the removal of accumulated sludges from the tanks. Such methods and equipment have been described in U.S. Pat. Nos. 4,945,933, 4,817,653, 5,091,016, 5,460,331 and 4,407,678, for example. While each of these patents described successful means for handling the sludges in various ways, another problem has existed with respect to sour crude oil storage that is not addressed by any of the aforementioned art and, yet, creates an extremely hazardous situation for ultimate cleaning of storage tanks requiring the entry of work people into the tanks. This problem is the accumulation of dangerous hydrogen sulfide gas and for carcinogen benzene vapors in the tank.
An environmental concern has also developed in connection with soils contaminated with volatile hazardous chlorinated hydrocarbon gases, such as ethylene dichloride. Often the only containment alternative for solids contaminated with ethylene dichloride is by using an enclosed hydrocarbon storage tank as a holding vessel for such contaminated soils. As the soil lies in the tank, the volatile chlorinated hydrocarbon, especially ethylene dichloride, permeates the atmosphere within the tank creating a dangerous situation of proportions equal to that of the hydrogen sulfide invasion of the contained atmosphere of a hydrocarbon storage tank.
Additionally, the entry of a worker into an atmosphere of these gases requires care equal to that of the care required in an atmosphere invaded by hydrogen sulfide. Many attempts have been made to avoid the necessity of entry into such tanks wearing heavy, hot and cumbersome equipment which burdens the worker to the extent that efficiency is lost and dangerous, life threatening work situations may occur, particularly in an enclosed atmosphere during hot periods of time such as summer along the Texas and Louisiana Gulf Coast, where many such tanks exist.
The ethylene dichloride problem is particularly troublesome since it is a material which, when contaminating soil, must be removed but, without adequate means of containment, becomes a complicated environmental problem. Soil contaminated with ethylene dichloride also presents a threat to the water supply. Since benzene, ethylene dichloride and the chlorinated hydrocarbons are somewhat water soluble, they leach from surface soil into progressively deeper areas of soil and ultimately end up in lakes and streams. Therefore, the contamination to be contained must be separated from the possibility of leaching caused by natural circumstances such as rain and weather. However, when so protected by putting it into closed containers, such as large storage tanks, the vapor pressure of VOCs and ethylene dichloride at elevated temperatures increases to the point where the entire atmosphere within such storage vessel is, in short time, permeated with the hazardous gas mixture.
Further, the captivity of such hazardous gases within the vapor atmosphere of such storage tanks creates a hazard in the neighborhood of such tanks because of the expansion and contraction of gases with changes in ambient temperature. A temperature rise causes the gases to exit through vents into the surrounding area and, while attempts are made to contain such exposure to gases, such as hydrogen sulfide and ethylene dichloride, through absorption in carbon canisters on such vents, high concentrations of such materials quickly saturate the carbon bed and cause breakthroughs into the surrounding area creating hazards of health and fire for even a slightly careless act.
It is an object of this invention to provide the removal of hazardous gases from the interior of closed vessels, particularly storage tanks, without requiting the entry of workers into the vessel.
It is a further object of this invention to provide a solution to both the contamination problem created by the storage of sour crude hydrocarbon and the atmospheric contamination problem created by the presence of large amounts of ethylene dichloride contamination in soil.
It is still a further object of this invention to provide a method whereby the hazardous gas containing atmosphere of a closed vessel can be removed from the tank with the hazardous gases being separated from the vapors of the storage tank, itself and contained for disposal.
It is still a further object of this invention to provide a method whereby soil contaminated with volatile organic hydrocarbons having water solubility can be cleaned without causing atmospheric contamination.